The present invention relates to an electromagnetic fuel injector and a method of producing the same. More particularly, the invention is concerned with an electromagnetic fuel injector suitable for use in automotive engines, and also to a method of producing such a fuel injector.
Japanese Patent Laid-Open Publication No. 119364/1985, particularly FIG. 1 of the drawings attached thereto, shows a typical known electromagnetic fuel injector.
The fuel injector has a movable valve part which is integrally composed of a ball valve 11, a plunger rod 10 and a plunger 7 which serves as a movable core. In operation, an electric current is supplied to a solenoid coil 4 so that a magnetic circuit is formed so as to include the plunger 7, a stator core 2 and a yoke 6 so that a magnetic attracting force is generated to enable the stator core 2 to attract the plunger 7. When the supply of the electric current to the solenoid coil 4 is cut off, the magnetic attracting force is extinguished so that the movable valve part is reset to the original position by the force of the spring 5.
Usually, the mechanical connection between the stator 2 and the yoke 6 is attained by caulking by means of a jig which is moved downward onto the brim of an opening in the yoke so as to plastically deform the material of the yoke simultaneously over the entire circumference of the opening in the yoke.
This connecting method, however, is disadvantageous in that the center of the caulking force applied to the peripheral region of the connecting portion tends to be deviated from the center of the opening in the yoke, so that a difficulty is encountered in uniformly caulking the yoke. The yoke also tends to be deformed to cause an offset between the axes of the yoke and the stator core in the assembled state.
Furthermore, since the precision of the construction of a fuel injector depends on the radial size of the stator core and the length of the surface at which the stator core is coupled to the yoke, the caulking method mentioned above inherently has a possibility of a large eccentricity, resulting in a large fluctuation of the assembly precision in the axial direction which often reaches 0.06 mm (see FIG. 4).
In the known fuel injector in which the yoke and the stator are fixed to each other by caulking, it is necessary that a valve guide and a plunger rod guide have large lengths in order to ensure a smooth and precise reciprocating movement of the movable core. The use of such long valve guide and long plunger rod guide inevitably increases the size of the fuel injector and complicates the construction of the same.